Semiconductor component and a method for producing the same

ABSTRACT

A semiconductor component, such as a humidity sensor, which has a semiconductor substrate, such as, for example, made of silicon, a first electrode and a second electrode and at least one first layer that is accessible for a medium acting from the outside on the semiconductor component, the first layer being arranged at least partially between the first and the second electrode. To reduce the costs for producing the semiconductor component the first layer has pores into which the medium reaches at least partially.

FIELD OF THE INVENTION

The present invention relates to a semiconductor component, such as, forexample, a humidity sensor, and a method for producing a semiconductorcomponent.

BACKGROUND INFORMATION

Multi-layer semiconductor components for ascertaining the quantityand/or the type of a medium acting on the semiconductor component mayhave a capacitor arrangement. The medium may act on a layer locatedbetween a first and a second electrode. In the case of a semiconductorcomponent which forms a humidity sensor, this may be the humidity in theair surrounding the semiconductor component. In a humidity sensor,atmospheric humidity may penetrate through a patterned top electrodeinto a moisture-sensitive layer and change the dielectric constant ofthis layer. This may lead to a moisture-dependent change in thecapacitance of the capacitor formed by the two electrodes and themoisture-sensitive layer, which may be evaluated.

SUMMARY OF THE INVENTION

In contrast, a semiconductor component according to an exemplaryembodiment of the present invention may have a layer which is providedwith pores and may be produced inexpensively. The medium to bedetermined qualitatively and/or quantitatively may get into it, therebychanging the dielectric constant of the porous layer. Such a layer maybe a silicon layer that is porous or is provided with pores. In contrastto other capacitive humidity sensors provided with a polymer layer, theporous layer of the semiconductor component according to an exemplaryembodiment of the present invention may exhibit no moisture-dependentswelling.

With a semiconductor component according to an exemplary embodiment ofthe present invention, using such a porous layer, a sensor may beinexpensively produced both for a gaseous and for a liquid medium,which, in addition, may be characterized by a desired durability andreliability. The semiconductor component may be built as a sensor fordetermining the atmospheric humidity.

An exemplary method according to the present invention may produce theat least one porous layer of the semiconductor component according tothe invention using one or more etching media containing hydrofluoricacid. The porosity in the starting layer of the semiconductor componentof the present invention for producing the porous layer may be producedby applying an electric field between the upper side and the lower sideof the semiconductor component, and an accompanying flow of electriccurrent through the etching medium or the etching media. The porosity,i.e. particularly the relationship of the total extent of the hollowspace of all pores to the volume of the remaining material of the layermay be adjusted in a simple, reproducible manner by applying a suitableelectric voltage. In particular, the etching process may be stoppedlargely abruptly with the switch-off of the voltage. The productionprocess may thereby be controlled in a desired manner.

According to an exemplary embodiment of the invention, the etchingmedium and/or the etching media for producing the pores may behydrofluoric acid (HF) or a liquid mixture or a chemical compound whichcontains hydrofluoric acid.

In one exemplary embodiment of the invention, a highly volatilecomponent, such as, for example, an alcohol such as ethanol, and/orpurified water may be added to the etching medium(s) to dilute it/them.

Ethanol is believed to reduce the surface tension of an etching mediumprovided with it, thereby permitting better wetting of the siliconsurface and a better penetration of the etching medium into etchedpores. Moreover, the bubbles developing during the etching process maybe smaller than without the addition of ethanol to the etching medium,and the bubbles may thus be able to escape better through the poresalready formed.

According to an exemplary embodiment of the invention, the etchingmedium, the HF-concentration in the etching medium and/or the doping ofthe region to be etched and/or the temperature and possibly otherprocess parameters of the etching method may be selected so that theetching process, i.e. the pore formation, may be adjusted in a suitablemanner and/or may be stopped, that is, for example, largely abruptly,with the switch-off of the electric voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a humidity sensor having a bottom electrode, a patternedtop electrode and an overetched polymer layer located between bothelectrodes—in cross-section.

FIG. 2 shows the preliminary stage of a first exemplary embodiment of ahumidity sensor according to the present invention—in cross-section.

FIG. 3 shows a first further development of the first exemplaryembodiment shown in FIG. 2—in cross-section.

FIG. 4 shows a second further development of the first exemplaryembodiment shown in FIG. 2—in cross-section.

FIG. 5 shows an exemplary embodiment of a humidity sensor from FIG. 3 or4, provided with electrical connections—in cross-section and in planview.

FIG. 6 shows a first variant of a second exemplary embodiment of ahumidity sensor according to the present invention, having twoelectrodes arranged at the same level and a screening electrode locatedabove them—in cross-section.

FIG. 7 shows the humidity sensor shown in FIG. 6 without screeningelectrode—in cross-section.

FIG. 8 shows the humidity sensor shown in FIG. 6 without screeningelectrode and without intermediate layer—in cross-section.

FIG. 9 shows a first exemplary embodiment for the bottom electrodes,shown in FIGS. 6 through 8, in the form of a plate-type capacitor—inplan view.

FIG. 10 shows a second exemplary embodiment for the bottom electrodes,shown in FIGS. 6 through 8, in the form of an interdigital structureformed by two intermeshing comb-type electrodes—in plan view.

FIG. 11 shows another humidity sensor according to an exemplaryembodiment of the present invention which has a reticular upperelectrode and a reticular lower electrode—in cross-section.

DETAILED DESCRIPTION

Humidity sensor 100, shown in FIG. 1, has a silicon substrate 101, abottom electrode or lower electrode 102 formed by a suitably dopedregion in silicon substrate 101, an overetched polymer layer 103 and apatterned top electrode 104. Air reaches polymer layer 103 via thepatterning or openings in patterned top electrode 104. The moisturecontained in the air reaches polymer layer 103 and influences itsdielectric constant. The dielectric constant of polymer layer 103 may bedetermined via lower electrode 102, polymer layer 103 and patterned topelectrode 104 which form a plate-type capacitor. The instantaneousatmospheric humidity may be ascertained on the basis of the dielectricconstant.

Changing atmospheric humidity may lead to shrinking or swelling of thepolymer layer, which after some time may result in mechanicaldestruction of humidity sensor 100. In addition, the construction of thehumidity sensor using a polymer may require considerable outlay and maytherefore be costly for a mass-produced product, particularly in theautomobile sector.

Preliminary stage 200 of a first exemplary embodiment of a humiditysensor according to the present invention shown in FIG. 2 has a siliconsubstrate 101, a bottom electrode or lower electrode 102 formed by adoped region, a so-called intermediate layer 201 made of silicondeposited on the upper side of silicon substrate 101 and doped region102, a top electrode or upper electrode 202 formed by a doped region,and a masking, formed by a mask layer 203, of the upper side ofintermediate layer 201. The masking of the upper side of intermediatelayer 201 is such that an etch opening 204 is formed above lowerelectrode 102, intermediate layer 201 and upper electrode 202.Preliminary stage 200 may be produced by a silicon semiconductorprocess.

To produce a perforated or porous top electrode 202 as well as aperforated or porous intermediate layer 201, in each case, for example,restricted to the region below etch opening 204, preliminary stage 200shown in FIG. 2 may be put into an etching medium that, for example,contains hydrofluoric acid. An electric voltage is applied between theupper side of preliminary stage 200 and the lower side of preliminarystage 200. The electric voltage may cause current to flow in the etchingmedium which may produce pores or openings in top electrode 202 andsubsequently in intermediate layer 201, in each case largely restrictedto the region below etch opening 204. A result of the electrochemicaletching using hydrofluoric acid is first further development 300, shownin FIG. 3, of the first exemplary embodiment shown in FIG. 2. Theprocess parameters have been set during the etching so that the porosityof the relevant region of top electrode 202 and of relevant region 301of intermediate layer 201 are substantially identical. Porosity isunderstood to be influenced by the relationship of cavity space or spaceaccessible from the outside, which is given by the pores formed in therelevant regions, to the volume of the remaining material of the layerspecific to a volumetric unit.

Production of a top electrode 202 whose porosity may be substantiallythe same as the porosity of intermediate layer 201, located below andnext to it, in relevant regions 301, may be achieved according to thepresent invention in that the intensity of the current flowing throughthe etching medium when producing the pores in top electrode 202 andsubsequently when producing the pores in intermediate layer 201 arrangedbelow it is largely identical. If desired, when adjusting the currentintensity for producing the porosity in top electrode 202, it may berequired to be taken into account that region 202 is doped differentlyfrom intermediate layer 201. Given etching parameters which areotherwise constant, the depth of the porous etching may be predeterminedby the period of time during which the electric current flows throughthe etching medium.

The humidity sensor according to an exemplary embodiment of the presentinvention shown in FIG. 3 forms a capacitor having a porous, thin, upperelectrode 202 and a porous region 301 in intermediate layer 201 betweenupper electrode 202 and lower electrode 102. Porous region 301 ofintermediate layer 201 supports upper electrode 202. Humid air may getinto porous region 301 of intermediate layer 201 through the fine poresof thin, upper electrode 202, relative to the thickness of intermediatelayer 201. Therefore, the dielectric constant, and thus the evaluablecapacitance between the upper and lower electrodes may change as afunction of the specific atmospheric humidity.

The controlled utilization of the dependence of the form of the porosityon the doping may also be provided. For example, by using an n-dopingfor the upper electrode, one may obtain vertical pores, and by using ap-doping for the intermediate layer, one may obtain finely branchedpores.

As will be explained in greater detail later in connection with FIG. 5,the two electrodes may be electrically connected via doped regions inthe form of printed circuit traces to contact pads or contact areas, orto a circuit (not shown) integrated on the sensor. In addition, areference capacitor may be produced on the sensor that, for example, iscovered over the entire surface with metal during the subsequentmetallization step. Alternatively, the covering may also be implementedby a passivation applied separately. In this manner, the referencecapacitor may no be longer sensitive to moisture.

FIG. 4 shows a second further development of the preliminary stage of afirst exemplary embodiment shown in FIG. 2. In contrast to the firstfurther development, shown in FIG. 3, of the preliminary stage of afirst exemplary embodiment shown in FIG. 2, in region 401 of upperelectrode 202 or of upper intermediate layer 201, the humidity sensoraccording to an exemplary embodiment of the present invention shown inFIG. 4 has a porosity which is perceptibly less than the porosity ofintermediate layer 201 located below upper electrode 202. To achievethis, upper electrode 202, i.e. the corresponding doped region whichforms the upper electrode, may be porously etched in a time-controlledmanner by applying an electric voltage in hydrofluoric acid. In sodoing, work may be performed using a low current density to cause a lowporosity. After intermediate layer 201 has been porously etched in theregion of upper electrode 202, the current density is markedlyincreased. The underlying intermediate layer is now likewise porouslyetched, but with a perceptibly higher porosity compared to the porosityof upper electrode 202. The porously etched regions are delimitedlaterally by mask layer 203. In contrast to the first furtherdevelopment, intermediate layer 201 is markedly more porous than thedoped region or the doped layer which forms upper electrode 202, asalready explained. The feature in this exemplary embodiment of thepresent invention is that the change in the dielectric constant inresponse to a change in the atmospheric humidity, which acts on thehumidity sensor of the present invention, happens primarily—asdesired—in intermediate layer 201 or in the intervening space betweenthe upper and lower electrodes. Care may be required to be taken in theporous etching of the present invention that the porous residualmaterial in the intervening space between the upper and lower electrodesis still stable enough that it provides sufficient mechanical supportfor the upper electrode.

FIG. 5 shows, in cross-section and in plan view, the exemplaryembodiment of a humidity sensor 500 from FIG. 3 or 4, provided withelectrical connections. Lower electrode 102 is connected via a suitableplated-through hole 501 to a contact area 502 for its externalcontacting. Upper electrode 202 is connected via a suitable contact deck504 to a contact area 503 for its external contacting. The capacitanceof the capacitor formed by upper electrode 202, lower electrode 102 andporous layer 301 or 402 located in between is determined via theexternal contactings. As already explained, the dielectric constant ofthe porous layer arranged between the two electrodes is a function ofthe specific medium which is able to penetrate from the outside into thepores of the porous layer. In the same manner, the dielectric constantof the porous layer is a function of the concentration of the medium inquestion. In the example of a humidity sensor described here,atmospheric humidity penetrates via porous upper electrode 202 intoporous region 301 or 402, so that the capacitance of the capacitorchanges. This change is supplied via contact areas 502 and 503 to anevaluation circuit (not shown) which ascertains or quantitativelydetermines the capacitance change and the changed atmospheric humiditygiving rise to it. To this end, a reference capacitor may be used, forexample, which is likewise integrated on the semiconductor component(not shown).

While the upper part of FIG. 5 shows humidity sensor 500 incross-section, the lower part of FIG. 5 shows humidity sensor 500 inplan view. It may be inferred from the plan view of humidity sensor 500that lower electrode 102 and upper electrode 202 have a rectangularoutline, and are arranged in parallel, displaced in height relative toeach other. Their outlines largely coincide.

First variant 600 of a second exemplary embodiment of a humidity sensoraccording to the present invention shown in FIG. 6 has two electrodes601 and 602 arranged at the same level. It may be inferable from thecross-section of the first variant, i.e. from semiconductor component600 shown in FIG. 6 that first electrode 601 and second electrode 602are covered by a screening electrode 603. Screening electrode 603, theregion of intermediate layer 201 below screening electrode 603 and theregion between first electrode 601 and second electrode 602 have beenmade porous in the manner described. In the example of a humidity sensorpresented here, atmospheric humidity gets between first electrode 601and second electrode 602 via the pores in screening electrode 603, theporous region (not shown) of intermediate layer 201 and the porousregion (not shown) between electrodes 601 and 602. The dielectricconstant of the porous region between first electrode 601 and secondelectrode 602 thereby changes, so therefore the capacitance of thedescribed capacitor changes. The change in capacitance may be evaluatedfor the quantitative determination of the atmospheric humidity.

FIG. 7 shows the humidity sensor of the present invention depicted inFIG. 6 without screening electrode 603. Like the exemplary embodimentshown in FIG. 6, the exemplary embodiment of a semiconductor component700 shown in FIG. 7 has an intermediate layer 201 that has been madeporous by the aforesaid measures in the region of first electrode 601and second electrode 602. In the same manner, the region between firstelectrode 601 and second electrode 602 of exemplary embodiment 700 inFIG. 7 is porous, so that atmospheric humidity acting from outside onsemiconductor component 700 leads to a change in the dielectric constantof the layer between the two electrodes 601 and 602, which may beevaluated in the manner described for the quantitative ascertainment ofthe atmospheric humidity.

Humidity sensor 800 shown in FIG. 8 differs from the exemplaryembodiment shown in FIG. 6, in that it has neither a screening electrode603 (see FIG. 6) nor a porous intermediate layer 201 (see FIG. 7). Thus,humidity sensor 800 shown in FIG. 8 has only a silicon substrate 101 andtwo suitably doped regions which form first electrode 601 and secondelectrode 602. Humidity sensor 800 again has a porous region or a porouslayer (not explicitly shown) between the two electrodes 601 and 602. Inthe same manner as for the semiconductor component shown in FIG. 6 andFIG. 7, atmospheric humidity acting on humidity sensor 800 from theoutside gets between the two electrodes 601 and 602 and changes thedielectric constant of the porous layer arranged between the twoelectrodes. The accompanying change in capacitance may be detected forascertaining the atmospheric humidity currently acting on the humiditysensor.

FIG. 9 shows a first exemplary embodiment 900 for the electrodes, shownin cross-section in FIGS. 6 through 8, which form a plate-typecapacitor. Plate-type capacitor 900 has a first bottom electrode 901 anda second bottom electrode 902.

FIG. 10 shows a second exemplary embodiment for the electrodes shown incross-section in FIGS. 6 through 8. They have the form of twointermeshing comb-type electrodes 1001 and 1002 which form a so-calledinterdigital structure 1000.

FIG. 11 shows another humidity sensor 1100 according to the presentinvention—in cross-section. Silicon substrate 1101 and siliconintermediate layer 1102 of FIG. 11 have a suitable p-doping. On p-dopedsilicon substrate 1101, a—in plan view (not shown)—reticular or latticedlower electrode, which is designated by 1103 in the cross-sectionaldrawing, has been formed by an n-doped region, corresponding to thisform, in silicon substrate 1101.

P-doped silicon intermediate layer 1102 has been deposited on siliconsubstrate 1101 and the n-doped region, i.e. lower electrode 1103.Silicon intermediate layer 1102 is likewise provided with an n-doping sothat, in turn, an n-doped region is formed. The n-doped region in turnforms a—in plan view (not shown)—reticular or latticed upper electrodedesignated in the cross-sectional drawing of FIG. 11 by 1104. Theproduction of the n-doped regions and the deposition of the intermediatelayer may be carried out in known manner, so that it is not necessary todiscuss it in greater detail.

To produce porous region 301 of FIG. 11, the structure of FIG. 11described above is etched electrochemically in the manner alreadydescribed. Because of the voltage difference between the upper side andthe lower side of the structure shown in FIG. 11, during the etchingprocess, an electric current flows which, starting from the etchingmedium surrounding the structure of FIG. 11, flows substantiallyuniformly through p-doped, epitactically deposited intermediate layer1102, and flows past the n-doped electrodes without penetrating them.Expressed differently, the current density in the n-doped electrodes islargely negligible compared to the current density in intermediate layer1102. The result is that, during the etching process, pores are formedalmost exclusively in layer 1102 and not in latticed electrodes 1103 and1104. That is to say, only intermediate layer 1102 is porous below etchopening 204 in the etch mask; in contrast, electrodes 1103 and 1104 arenot, or are largely not porous. Porous region 301 in intermediate layer1102 is then used in the manner already described for the quantitativeand/or qualitative determination of the medium like, in particular, airwhich has penetrated from above into the intermediate layer. Themoisture or water content of the air may be determined capacitively withthe aid of the structure, shown in FIG. 11, which, in particular, isintended to form a humidity sensor according to an exemplary embodimentof the present invention. N-doped electrodes 1103 and 1104 of thepresent invention may be characterized in that they are not affectedduring the electrochemical etching. Therefore, their electricconductivity may be largely retained in spite of the etching process (nomaterial removal). In addition, leakage currents may be substantiallyavoided by the use of n-doped electrodes in p-doped material such as, inparticular, silicon.

The List of Reference Numerals is as follows: 100 known humidity sensor;101 silicon substrate; 102 bottom electrode, lower electrode, formed bysuitably doped region; 103 overetched polymer layer; 104 patterned topelectrode, upper electrode; 200 preliminary stage of a first specificembodiment of a humidity sensor according to the present invention; 201silicon intermediate layer; 202 top electrode, upper electrode, dopedregion; 203 mask layer; 204 etch opening; 300 first variant of the firstspecific embodiment shown in FIG. 2; 301 porous region in intermediatelayer 201, which extends in the entire region below etch opening 204 upto bottom electrode 102; 400 second variant of the first specificembodiment shown in FIG. 2; 401 region having low porosity, whichextends in the region below etch opening 204 up to approximately thelower side of top electrode 202; 402 region having great porosity, inrelation to region 401, which extends in the region below etch opening204 up to approximately the lower side of bottom electrode 102; 500exemplary embodiment of a humidity sensor from FIG. 3 or 4, providedwith electrical connections, in cross-section and in plan view; 501plated-through hole; 502 contact area for contacting of the bottomelectrode; 503 contact area for contacting of the top electrode; 504contact deck for contacting of the top electrode; 600 first variant of asecond specific embodiment of a humidity sensor according to the presentinvention, having two electrodes arranged at the same level and ascreening electrode located above them; 601 first bottom electrode; 602second bottom electrode; 603 screening electrode; 700 the humiditysensor of the present invention shown in FIG. 6 without screeningelectrode; 800 the humidity sensor of the present invention shown inFIG. 6 without screening electrode and without intermediate layer; 900 afirst specific embodiment for the electrodes, shown in FIGS. 6 through8, in the form of a plate-type capacitor; 901 first bottom electrode;902 second bottom electrode; 1000 a second specific embodiment for theelectrodes, shown in FIGS. 6 through 8, in the form of an interdigitalstructure formed by two intermeshing comb-type electrodes; 1001 firstbottom electrode in the form of a comb; 1002 second bottom electrode inthe form of a comb; 1100 example of a further specific embodiment of ahumidity sensor according to the present invention having reticular orlatticed electrodes; 1101 p-doped silicon substrate; 1102 p-dopedsilicon intermediate layer; 1103 reticular lower electrode; 1104reticular upper electrode.

1. A semiconductor component, comprising: a semiconductor substrate; afirst electrode; a second electrode; at least one first layer arrangedat least partially between the first electrode and the second electrode,the first layer being accessible for a medium acting from an outside onthe semiconductor component and having pores into which the medium isreachable at least partially, wherein at least one of the firstelectrode and the second electrode are formed at least partially by atleast one of a suitably doped semiconductor layer and a metallic layer;and a second porous layer having a porosity is less than a porosity of afirst porous layer, the second porous layer forming the first electrode,via which the medium one of completely and partially reaches the firstporous layer.
 2. The semiconductor component of claim 1, wherein thesemiconductor component functions as a humidity sensor.
 3. Thesemiconductor component of claim 1, wherein the semiconductor substrateincludes silicon.
 4. The semiconductor component of claim 1, wherein themedium is one of gaseous and liquid.
 5. The semiconductor component ofclaim 1, wherein the medium includes air having humidity.
 6. Thesemiconductor component of claim 1, wherein the porosity of the secondporous layer is influenced by a relationship of a volume of pores to amaterial of the second porous layer.
 7. The semiconductor component ofclaim 1, wherein the first and the second electrodes are arrangedessentially on the same level with a distance to one another.
 8. Asemiconductor component, comprising: a semiconductor substrate; a firstelectrode; a second electrode; and at least one first layer arranged atleast partially between the first electrode and the second electrode,the first layer being accessible for a medium acting from an outside onthe semiconductor component and having pores into which the medium isreachable at least partially, wherein at least one of the firstelectrode and the second electrode are formed at least partially by atleast one of a suitably doped semiconductor layer and a metallic layer,wherein: the first and the second electrodes are arranged essentially onthe same level with a distance to one another, and the first and secondelectrodes form an interdigital structure.
 9. A semiconductor component,comprising: a semiconductor substrate; a first electrode; a secondelectrode; at least one first layer arranged at least partially betweenthe first electrode and the second electrode, the first layer beingaccessible for a medium acting from an outside on the semiconductorcomponent and having pores into which the medium is reachable at leastpartially; and a third porous layer to at least one of cover and protectat least one of the first electrode, the second electrode, and a firstporous layer, wherein the first and second electrodes form aninterdigital structure.
 10. A method for producing a semiconductorcomponent, comprising: forming, by an etching medium, at least oneporous layer arranged at least partially between a first electrode and asecond electrode of the semiconductor component so that the at least oneporous layer is accessible for a medium acting from an outside on thesemiconductor component and includes pores into which the medium isreachable at least partially, wherein the at least one porous layer isformed by applying an electric field between an upper side and a lowerside of the semiconductor component and setting of electric currentwhich flows through the etching medium.
 11. The method of claim 10,wherein the etching medium includes one of hydrofluoric acid and HFacid.
 12. The method of claim 10, further comprising: providing theetching medium with at least one additive.
 13. A method for producing asemiconductor component, comprising: forming, by an etching medium, atleast one porous layer arranged at least partially between a firstelectrode and a second electrode of the semiconductor component so thatthe at least one porous layer is accessible for a medium acting from anoutside on the semiconductor component and includes pores into which themedium is reachable at least partially; and providing the etching mediumwith at least one additive-wherein the additive at least one of reducesbubble formation, improves a wetting, and improves a drying.
 14. Themethod of claim 13, wherein the additive includes an alcohol.
 15. Themethod of claim 14, wherein the alcohol includes ethanol.
 16. The methodof claim 15, wherein the concentration of the ethanol is approximately30% to approximately 90%.
 17. A method for producing a semiconductorcomponent, comprising: forming, by an etching medium, at least oneporous layer arranged at least partially between a first electrode and asecond electrode of the semiconductor component so that the at least oneporous layer is accessible for a medium acting from an outside on thesemiconductor component and includes pores into which the medium isreachable at least partially wherein at least one of a measure of aporosity of the at least one porous layer and an extent of pores of theat least one porous layer is controlled by at least one of a currentdensity of the etching medium, a concentration of hydrofluoric acid inthe etching medium, one or more additives to the etching medium, atemperature, a doping, and a duration of the current flow.